U.S. patent number 8,625,111 [Application Number 13/381,032] was granted by the patent office on 2014-01-07 for optical film thickness meter and thin film forming apparatus provided with optical film thickness meter.
This patent grant is currently assigned to Shincron Co., Ltd.. The grantee listed for this patent is Yohei Hinata, Yousong Jiang, Yoshiyuki Otaki, Kyokuyo Sai. Invention is credited to Yohei Hinata, Yousong Jiang, Yoshiyuki Otaki, Kyokuyo Sai.
United States Patent |
8,625,111 |
Sai , et al. |
January 7, 2014 |
Optical film thickness meter and thin film forming apparatus
provided with optical film thickness meter
Abstract
An optical film thickness meter capable of measuring an optical
film thickness and spectroscopic characteristics highly accurately,
and a thin film forming apparatus with the optical film thickness
meter are provided. The optical film thickness meter includes a
light projector, a light receiver, a monochromator, and a
reflection mirror having a reflection surface substantially
perpendicularly to the optical axis of measurement light on the
side opposite to an actual substrate. The actual substrate is
disposed having a predetermined angle to the optical axis. The
measurement light passes through the actual substrate twice,
whereby a change in transmissivity can be increased, and control
accuracy of thickness measurement is improved. Measurement errors
caused by a difference in transmission positions is prevented.
Since the measurement light which has not passed through the
measurement substrate twice is not detected by the light receiver,
the optical film thickness and spectroscopic characteristics is
measured highly accurately.
Inventors: |
Sai; Kyokuyo (Kanagawa,
JP), Hinata; Yohei (Kanagawa, JP), Otaki;
Yoshiyuki (Kanagawa, JP), Jiang; Yousong
(Kanagawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sai; Kyokuyo
Hinata; Yohei
Otaki; Yoshiyuki
Jiang; Yousong |
Kanagawa
Kanagawa
Kanagawa
Kanagawa |
N/A
N/A
N/A
N/A |
JP
JP
JP
JP |
|
|
Assignee: |
Shincron Co., Ltd.
(Yokohama-Shi, JP)
|
Family
ID: |
43411040 |
Appl.
No.: |
13/381,032 |
Filed: |
June 29, 2010 |
PCT
Filed: |
June 29, 2010 |
PCT No.: |
PCT/JP2010/061041 |
371(c)(1),(2),(4) Date: |
December 27, 2011 |
PCT
Pub. No.: |
WO2011/001968 |
PCT
Pub. Date: |
January 06, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120105872 A1 |
May 3, 2012 |
|
Foreign Application Priority Data
|
|
|
|
|
Jul 3, 2009 [JP] |
|
|
2009-158798 |
|
Current U.S.
Class: |
356/630;
356/625 |
Current CPC
Class: |
C23C
14/34 (20130101); G01B 11/06 (20130101); C23C
14/547 (20130101); G01B 11/0625 (20130101) |
Current International
Class: |
G01B
11/28 (20060101) |
Field of
Search: |
;356/625-632,504,503,485,492 ;250/559.27,559.28,559.4,559.19 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
54-91263 |
|
Jul 1979 |
|
JP |
|
56-44802 |
|
Apr 1981 |
|
JP |
|
59-72010 |
|
Apr 1984 |
|
JP |
|
6-11442 |
|
Jan 1994 |
|
JP |
|
2003-121119 |
|
Apr 2003 |
|
JP |
|
2004-219108 |
|
Aug 2004 |
|
JP |
|
2005-301032 |
|
Oct 2005 |
|
JP |
|
2006-45673 |
|
Feb 2006 |
|
JP |
|
2006-330485 |
|
Dec 2006 |
|
JP |
|
2007-199084 |
|
Aug 2007 |
|
JP |
|
02/063064 |
|
Aug 2002 |
|
WO |
|
Other References
International Search Report dated Aug. 24, 2010 in PCT application
PCT/JP2010/061041. cited by applicant .
International Preliminary Report on Patentability dated Feb. 14,
2012 in PCT application PCT/JP2010/061041. cited by applicant .
Office action dated Apr. 19, 2011 in corresponding Japanese Patent
Application 2009-158798. cited by applicant .
Taiwanese Office Action notified on Sep. 18, 2012. cited by
applicant .
Korean Office Action of Korean Patent Application No.
10-2012-7002789, issued on Apr. 30, 2013. cited by
applicant.
|
Primary Examiner: Ton; Tri T
Attorney, Agent or Firm: Novak Druce Connolly Bove + Quigg
LLP
Claims
The invention claimed is:
1. An optical film thickness meter which measures an optical film
thickness by allowing measurement light to pass through an actual
substrate, comprising: a light projector which emits outgoing light
as the measurement light toward the actual substrate; a reflection
mirror which reflects the outgoing light at a position on a side
opposite to the light projector relative to the actual substrate; a
light receiver which receives the measurement light which passes
through the actual substrate, is reflected by the reflection
mirror, and passes through the actual substrate; and a light
detector which detects the measurement light received by the light
receiver, wherein the actual substrate is disposed between the
reflection minor and the light projector so that a perpendicular
line to a film formation surface of the actual substrate has a
predetermined angle with respect to an optical axis of the
measurement light so that the light receiver receives the
measurement light having passed through a first path of the actual
substrate, reflected by the reflection mirror and then having
passed through a second path of the actual substrate a second time,
wherein at least one spot on the actual substrate in the first path
is the same as at least one spot on the actual substrate of the
second path.
2. The optical film thickness meter according to claim 1, wherein
the reflection mirror has a reflection surface formed substantially
in a perpendicular direction to the optical axis of the measurement
light.
3. The optical film thickness meter according to claim 2, wherein
the reflection mirror is disposed so that an angle formed by a
perpendicular line to the reflection surface of the reflection
mirror and the optical axis of the measurement light is within a
range of -5.0.degree. to +5.0.degree..
4. The optical film thickness meter according to claim 1, wherein
the predetermined angle with respect to an optical axis of the
measurement light is at least 4.5.degree..
5. The optical film thickness meter according to claim 1, wherein
the actual substrate moves at a predetermined speed, and the
reflection mirror is disposed in a fixed manner at a given position
with respect to the actual substrate.
6. A thin film forming apparatus, comprising: a dome-shaped
substrate holder which holds an actual substrate within a vacuum
container and is rotatable; a correcting plate disposed in a fixed
manner on a vacuum container side at a position between a
deposition device which vaporizes a deposition material and the
substrate holder; and an optical film thickness meter which
measures an optical film thickness by allowing measurement light to
pass through the actual substrate in a state in which the actual
substrate is mounted on the substrate holder, wherein the optical
film thickness meter includes: a light projector which emits
outgoing light as the measurement light toward the actual
substrate; a reflection mirror which reflects the outgoing light at
a position on a side opposite to the light projector relative to
the actual substrate; a light receiver which receives the
measurement light which passes through the actual substrate, is
reflected by the reflection mirror, and passes through the actual
substrate; and a light detector which detects the measurement light
received by the light receiver, wherein the actual substrate is
disposed with inclination with respect to an optical system
comprised of the light projector and the reflection mirror.
7. The thin film forming apparatus according to claim 6, wherein
the reflection mirror is disposed on the correcting plate.
8. The optical film thickness meter according to claim 1, wherein
the actual substrate moves at a predetermined speed, and the
reflection mirror is disposed in a fixed manner at a given position
with respect to the actual substrate.
9. The optical film thickness meter according to claim 2, wherein
the actual substrate moves at a predetermined speed, and the
reflection mirror is disposed in a fixed manner at a given position
with respect to the actual substrate.
10. The optical film thickness meter according to claim 3, wherein
the actual substrate moves at a predetermined speed, and the
reflection mirror is disposed in a fixed manner at a given position
with respect to the actual substrate.
11. The optical film thickness meter according to claim 4, wherein
the actual substrate moves at a predetermined speed, and the
reflection mirror is disposed n a fixed manner at a given position
with respect to the actual substrate.
Description
TECHNICAL FIELD
The present invention relates to an optical film thickness meter
and a thin film forming apparatus provided with the optical film
thickness meter and particularly to an optical film thickness
meter, which can measure film thickness with high accuracy and a
thin film thickness forming apparatus provided with the optical
film thickness meter.
BACKGROUND ART
For improvement of control accuracy of optical devices, improvement
of accuracy of a film thickness of an optical thin film is in
demand. For the highly accurate film thickness control of the
optical thin film, measurement is indispensable, and various types
of film thickness measurement methods and film thickness meters
used for the film thickness control have been proposed. It is
preferable that an optical film thickness meter excellent in
responsiveness and the like is used for the film thickness
measurement. The film thickness here means the film thickness of an
optical thin film and has a value depending on the physical film
thickness and refraction index.
The optical film thickness meter can be roughly divided into a
reflection type and a transmission type. The reflection type is a
technology for measuring the film thickness by using a phenomenon
of interference caused by generation of a phase difference due to a
difference between a path of a light beam reflected on the surface
of the optical thin film and a path of a light beam reflected on an
interface between a substrate and the optical film, and since
reflectance as the entire light beam cyclically changes with
respect to the film thickness, this technology is often used if the
number of formed films is small or if a relative measurement can be
used and has nonconformity in which use applications are relatively
limited.
On the other hand, the transmission type is, as illustrated in FIG.
9, a technology in which light emitted from a projector 11 is
reflected on a mirror 105 disposed in a mirror box 107 so that the
light beam transmitted through the optical thin film is measured,
and both the film thickness and spectroscopic characteristics can
be acquired from the transmissivity of the light amount. Since this
technology is hardly susceptible to a change in the light amount
caused by a change in an angle of an actual substrate S, it has an
advantage that measurement can be performed with high accuracy.
However, since a substrate for a monitor is used and the substrate
for a monitor is arranged at a position different from a position
of the actual substrate, a film-thickness difference is present
between the substrate for a monitor and the actual substrate, and
an experience and knowledge of a staff in charge of film formation
are needed for correcting the film-thickness difference, which
results in an instability factor in a film forming process and also
nonconformity of occurrence of a film thickness control error.
Also, the prior-art optical film thickness meter is mounted on a
thin film forming apparatus 3 as illustrated in FIG. 9, and it is
difficult to improve measurement accuracy for a film with low
refraction index. For example, SiO.sub.2 often used as a deposition
material has a small refraction index difference from monitor
glass, and particularly in a transmission photometric system, a
change amount in light amount in the in-situ measurement is small
and control is difficult, which are disadvantageous. That is, if
the change amount in light amount is small, control is forced to be
executed on the basis of a limited change amount, and improvement
of accuracy is made difficult.
In order to solve the above problems, a technology in which a light
beam (outgoing light) having passed through a measurement substrate
is reflected by a corner cube prism and the light beam (reflection
light) having passed through the measurement substrate again is
measured so as to measure the film thickness and the like is
proposed (See Patent Document 1, for example).
Patent Document 1: Japanese Patent Laid-Open No. 2006-45673
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
However, with the technology described in Patent Document 1, since
the light (outgoing light) having passed through the measurement
substrate is reflected by the corner cube prism, transmission
positions of the outgoing light and the reflection light are
different from each other in the measurement substrate, and due to
the difference in a portion for transmission measurement, there is
nonconformity that a measurement error occurs by micro thin film
distribution. Also with this technology, it is necessary to form a
reflection protective film (AR film) so that all the reflection
light can be used for measurement, and unless the AR film is formed
on each surface, a multiple reflection portion between the
substrate and the corner cube prism is also measured, and accurate
measurement cannot be made, which is nonconformity.
An object of the present invention is to provide an optical film
thickness meter, which can measure an actual substrate and
minimizes an error of a measurement position and a thin film
forming apparatus provided with the optical film thickness meter.
Also, another object of the present invention is to provide an
optical film thickness meter capable of measurement of optical film
thickness and spectroscopic characteristics with high accuracy
without requiring an AR film for measurement and a thin film
forming apparatus provided with the optical film thickness
meter.
Means for Solving Problem
According to an optical film thickness meter according to the
present invention, the above problems are solved by an optical film
thickness meter which measures an optical film thickness by
allowing measurement light to pass through an actual substrate,
provided with light projecting means which emits outgoing light as
the measurement light toward the actual substrate; a reflection
mirror which reflects the outgoing light at a position on the side
opposite to the light projecting means relative to the actual
substrate; light receiving means which receives the measurement
light which has passed through the actual substrate, been reflected
by the reflection mirror and passed through the actual substrate;
and light detecting means which detects the measurement light
received by the light receiving means, in which the actual
substrate is disposed with inclination with respect to an optical
system comprised of the light projecting means and the reflection
mirror.
As described above, since the optical film thickness meter makes
measurements by using measurement light which has passed through
the actual substrate, been reflected by the reflection mirror and
passed through the actual substrate, the measurement light
(outgoing light and reflection light) passes through the actual
substrate twice, whereby a change amount of transmissivity (light
amount) can be increased, and control accuracy of the film
thickness measurement can be improved.
Also, since the actual substrate is disposed with inclination with
respect to the optical system comprised of the light projecting
means and the reflection mirror, only the measurement light
reflected by the reflection mirror passes through the actual
substrate, and the reflection light, which is generated by the
reflection and is disadvantageous for measurement can be
excluded.
In more detail the actual substrate is disposed with a
predetermined angle with respect to the optical axis of the
measurement light at a position between the reflection mirror and
the light projecting means.
The outgoing light and the reflection light reflected by the
reflection mirror, which are the measurement lights, pass through
substantially the same spot on the actual substrate, and thus, the
outgoing light and the reflection light, which are the measurement
lights before and after the reflection by the reflection mirror,
can pass the same spot on the actual substrate, respectively, and
occurrence of a measurement error caused by a difference in the
transmission positions can be prevented.
Also, the reflection mirror preferably has a reflection surface
formed substantially in the perpendicular direction to the optical
axis of the measurement light. As a result, the reflection mirror
can reflect the measurement light incident from the light
projecting means and having passed through the actual substrate
without a loss so that the light passes through the actual
substrate through the same path as the incident path again.
The reflection mirror is preferably disposed so that an angle
formed by a perpendicular line to the reflection surface of the
reflection mirror and an optical axis of the measurement light is
within a range of -5.0 to +5.0.degree..
In this case, since the light amount is ensured to such a degree
that the measurement accuracy is not affected by loss of the light
amount, a certain degree of freedom can be ensured for a mounting
position of the reflection mirror.
Also, the inclination with respect to the optical system formed of
the light projecting means and the reflection mirror of the actual
substrate is preferably about 4.5.degree. or more. In this case,
since light not having passed through the actual substrate through
the predetermined path (unnecessary reflection light) is not
detected by the light detecting means, only the transmitted light
of the substrate can be accurately measured.
Also, it is preferable that the actual substrate moves at a
predetermined speed, and the reflection mirror is disposed in a
fixed manner at a given position with respect to the actual
substrate. By fixing the reflection mirror as above, the optical
system is made stable.
Also, according to the thin film forming apparatus provided with
the optical film thickness meter of the present invention, the
above problems are solved by a thin film forming apparatus provided
with a dome-shaped substrate holder which holds the actual
substrate within a vacuum container and is rotatable; a correcting
plate disposed in a fixed manner on the vacuum container side at a
position between deposition means which vaporizes a deposition
material and the substrate holder; and an optical film thickness
meter which measures the optical film thickness by allowing
measurement light to pass through the actual substrate in a state
in which the actual substrate is mounted on the substrate holder,
in which the optical film thickness meter is provided with light
projecting means which emits outgoing light as the measurement
light toward the actual substrate; a reflection mirror which
reflects the outgoing light at a position on the side opposite to
the light projecting means relative to the actual substrate; light
receiving means which receives the measurement light which has
passed through the actual substrate, been reflected by the
reflection mirror and passed through the actual substrate; and
light detecting means which detects the measurement light received
by the light receiving means, in which the actual substrate is
disposed with inclination with respect to an optical system
comprised of the light projecting means and the reflection
mirror.
As described above, according to the present invention, a thin film
forming apparatus which can manufacture a substrate (optical
product) for which film thickness control of an actual substrate
has been sufficiently executed by the optical film thickness meter
can be provided.
The reflection mirror is preferably disposed on the correcting
plate and can reflect the measurement light by the reflection
mirror stably in the fixed state. Also, with the fixed correcting
plate, an influence of stray light from a deposition source or
plasma discharge is made difficult to be given.
According to the thin film forming apparatus of the present
invention, the above problems are solved by a thin film forming
apparatus provided with a substantially cylindrical substrate
holder which supports the actual substrate within the vacuum
container and is rotatable; sputtering means disposed outside the
substrate holder; and an optical film thickness meter which
measures the optical film thickness by allowing the measurement
light to pass through the actual substrate in a state in which the
actual substrate is mounted on the substrate holder, in which the
optical film thickness meter is provided with light projecting
means which emits outgoing light as the measurement light toward
the actual substrate; a reflection mirror which reflects the
outgoing light at a position on the side opposite to the light
projecting means relative to the actual substrate; light receiving
means which receives the measurement light having passed through
the actual substrate, having been reflected by the reflection
mirror and having passed through the actual substrate; and light
detecting means which detects the measurement light received by the
light receiving means, in which the actual substrate is disposed
with inclination with respect to an optical system comprised of the
light projecting means and the reflection mirror. In this case, the
reflection mirror is preferably disposed in the substrate
holder.
As described above, since the reflection mirror is arranged in the
substrate holder, the reflection mirror is difficult to be stained
and is hardly susceptible to the influence of stray light from the
plasma discharge in sputtering.
Effect of the Invention
According to the optical film thickness meter and the thin film
forming apparatus according to the present invention, since the
actual substrate itself can be measured, unlike measurement with a
monitor substrate, a measurement error or the like hardly occurs.
Also, the measurement light (outgoing light and reflection light)
passes the actual substrate twice, whereby the change amount of the
transmissivity (light amount) can be increased, and control
accuracy of the film thickness measurement can be improved. Also,
since the actual substrate is disposed with a predetermined angle
with respect to the optical axis of the measurement light, only the
measurement light reflected by the reflection mirror passes through
the actual substrate, and a portion of a reflection light of
multiple reflection generated between the reflection mirror and the
actual substrate can be removed.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a configuration explanatory diagram illustrating a thin
film forming apparatus provided with a rotary-drum type holder seen
from above;
FIG. 2 is a configuration explanatory diagram of a thin film
forming apparatus provided with a dome-shaped holder seen from the
side;
FIG. 3 is a graph illustrating a relationship between a reflection
mirror angle to an optical axis and measurement light
intensity;
FIGS. 4A and 4B are explanatory diagrams illustrating inclination
of a substrate and a rate change of the measurement light;
FIG. 5 are graphs illustrating a relationship between a substrate
angle and the measurement light intensity;
FIG. 6 is a graph illustrating a transmissivity measurement result
of a BK-7 substrate;
FIG. 7 is a graph illustrating the transmissivity measurement
result of an IR cut filter;
FIG. 8 is a graph of a calculation result of a light amount change
in an optical film thickness at a wavelength of 520 nm by time
elapse in the case of formation of a SiO.sub.2 single-layer film;
and
FIG. 9 is a configuration explanatory diagram of a thin film
forming apparatus provided with a prior-art transmission-type
optical film thickness meter.
EXPLANATIONS OF LETTERS OR NUMERALS
S actual substrate (measurement substrate)
F optical filter
L1 outgoing light
L2 (L2-1, L2-2, L2-3) reflection light
1, 2, 3 thin film forming apparatus
11 light projector
11a Ref circuit
13 optical fiber
13a optical fiber on the outgoing light side
13b optical fiber on the reflection light side
14 optical fiber end portion
15 spherical achromatic lens
17 reflection mirror
19 light receiver
20 monochromator
21 stabilized power supply for light source
23 computer (PC for calculation)
25 measurement window
31, 41, 101 vacuum container
33 rotary-drum holder
35 sputtering means
43, 103 rotary holder
45 deposition means
47 correcting plate
105 mirror
107 mirror box
BEST MODE(S) FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below by
referring to the attached drawings. Members, arrangement and the
like described below are one example which embodies the invention
and do not limit the present invention, and it is needless to say
that various alterations are possible along the gist of the present
invention.
FIGS. 1 and 2 illustrate an optical film thickness meter and a thin
film forming apparatus according to the present invention, in which
FIG. 1 is a configuration explanatory diagram illustrating a thin
film forming apparatus provided with a rotary-drum type holder seen
from above, and FIG. 2 is a configuration explanatory diagram of a
thin film forming apparatus provided with a dome-shaped holder seen
from the side.
Also, FIGS. 3 to 8 relate to an optical film thickness meter
according to the present invention, in which FIG. 3 is a graph
illustrating a relationship between a reflection mirror angle to an
optical axis and measurement light intensity, FIGS. 4A and 4B are
an explanatory diagram illustrating inclination of a substrate and
a rate change of the measurement light, FIG. 5 is a graph
illustrating a relationship between a substrate angle and the
measurement light intensity, FIG. 6 is a graph illustrating a
transmissivity measurement result of a BK-7 substrate, FIG. 7 is a
graph illustrating the transmissivity measurement result of an IR
cut filter, and FIG. 8 is a graph of a calculation result of a
light amount change in an optical film thickness at a wavelength of
520 nm by time elapse in the case of formation of a SiO.sub.2
single-layer film.
The optical film thickness meter according to the present invention
does not measure a monitor substrate dedicated for measurement but
measures the film thickness of an actual substrate (product) S as a
measurement substrate and includes, as illustrated in FIGS. 1 and
2, a light projector 11 as a light source or light projecting
means, an optical fiber 13 (13a and 13b) as light guiding means, a
spherical achromatic lens 15, a reflection mirror 17, and a light
receiver 19 as light receiving means. Also, a voltage is applied to
the light projector 11 through a stabilized power supply 21 for a
light source, and the light receiver 19 is connected to a computer
(PC for calculation) 23.
As illustrated in FIG. 4, in this description, measurement light
before being reflected by a reflection mirror 17 is described as
outgoing light L1 and the measurement light after being reflected
as reflection light L2 (L2-1, L2-2, L2-3) separately.
The light projector 11 is a device which outputs the outgoing light
L1 used for measurement and incorporates a Ref circuit 11a, and to
the light projector 11, electric power is supplied from the
stabilized power supply 21 for a light source and the light
projector 11 is constituted so as to emit the measurement light
having an arbitrary wavelength to an optical fiber 13a on the
outgoing light side.
The light receiver 19 is a device into which light having passed
through an actual substrate S, which is a measurement substrate, by
the outgoing light L1 is reflected by the reflection mirror 17 and
the reflection light L2 which passed through the actual substrate S
again is inputted through an optical fiber 13b on the reflection
light side.
The light receiver 19 is provided with a monochromator 20 as light
detecting means and is capable of measurement of a wavelength or
transmissivity of the measurement light and is connected to a
computer (PC for calculation) 23 which calculates and displays a
film thickness and optical characteristics of an optical thin film
on the basis of an analysis result by the monochromator 20.
The optical fiber 13 is comprised of a two-branch bundle fiber
formed of the optical fiber 13a on the outgoing light side and the
optical fiber 13b on the reflection light side and is collected in
a two-branch flexible tube made of stainless steel. The optical
fiber 13a on the outgoing light side has one end portion side
connected to the light projector 11, while the optical fiber 13b on
the reflection light side has one end portion side connected to the
light receiver 19. An optical fiber end portion 14 of each of the
optical fiber 13a on the outgoing light side and the optical fiber
13b on the reflection light side are collected into one bundle and
disposed having its optical axis oriented toward the spherical
achromatic lens 15 and the actual substrate S, which is a
measurement substrate. The outgoing light L1 emitted from the
optical fiber end portion 14 has a circular section having a
diameter of 5 to 6 mm.
The spherical achromatic lens 15 is a lens, which removes
aberration by the wavelength (chromatic aberration) and spherical
aberration and can improve measurement accuracy and is disposed
between the optical fiber end portion 14 and a measurement window
25 formed in the thin film forming apparatuses 1 and 2.
The reflection mirror 17 is disposed on the back side of the actual
substrate S and reflects the outgoing light L1 from the light
projector 11 having passed through the actual substrate S. For the
reflection mirror 17, a mirror coated with Al film or Ag film, a
mirror over-coated with MgF.sub.2 or SiO on the Al film or Ag film,
or a mirror over-coated with other dielectric films can be used.
The size of the reflection surface is arbitrary, but it is
preferable that the size is approximately equal to the size of the
actual substrate S, which is several centimeters. The reflection
surface of the reflection mirror 17 has reflectance of
approximately 80%. The reflection mirror 17 is disposed
substantially perpendicular (at a right angle) to the optical axis
of the outgoing light L1 emitted to the actual substrate S, and
thus, the reflected outgoing light L1 becomes the reflection light
L2, and the reflection light L2 passes through the actual substrate
S along the same path as the optical axis of the outgoing light
L1.
The spherical achromatic lens 15, the actual substrate S, and the
reflection mirror 17 are disposed along the optical axis of the
measurement light from the optical fiber end portion 14.
For the actual substrate S, a member formed of a material such as
glass is preferable. In this embodiment, a plate-shaped member is
used for the actual substrate S, but the shape of the actual
substrate S is not limited to such a plate shape. Also, other
shapes on the surface of which a thin film can be formed such as a
lens shape, a cylindrical shape, a ring shape or the like, for
example, can be used. Here, the glass material is a material formed
of silicon dioxide (SiO.sub.2), and specifically, quartz glass,
soda-lime glass, borosilicate glass and the like can be cited. The
actual substrate S in this embodiment is supposed to include an
optical filter F.
Also, the material of the actual substrate S is not limited to
glass but may be a plastic resin. Examples of the plastic resin
include a resin material selected from a group comprising of
polycarbonate, polyethylene terephthalate, polybutylene
terephthalate, acrylonitrile-butadiene-styrene copolymer, nylon,
polycarbonate-polyethylene terephthalate copolymer,
polycarbonate-polybutylene terephthalate copolymer, acryl,
polystyrene, polyethylene, and polypropylene or a mixture of these
materials and a glass fiber and/or a carbon fiber and the like.
Here, a path along which the measurement light (the outgoing light
L1 and the reflection light L2) radiated from the light projector
11 is inputted into the light receiver 19 will be described.
The outgoing light L1, which is the measurement light outputted
from the light projector 11, is radiated from the optical fiber end
portion 14 to the spherical achromatic lens 15 through the optical
fiber 13a on the light projection side, passes through the
measurement window 25 formed in the thin film forming apparatuses 1
and 2 and is radiated to the actual substrate S.
The outgoing light L1 radiated to the actual substrate S passes
through the actual substrate S, is reflected by the reflection
mirror 17 disposed on the back side of the actual substrate S and
becomes the reflection light L2. The reflection light L2 reflected
by the reflection mirror 17 passes through the actual substrate S,
the measurement window 25, and the spherical achromatic lens 15
again and reaches the optical fiber end portion 14. Then, only the
measurement light from the actual substrate S side (the reflection
light L2) passes through the optical fiber 13b on the reflection
light side and is led to the light receiver 19.
As will be described later, the actual substrate S is disposed so
as to have an inclination angle with respect to the optical axis of
the measurement light.
Subsequently, a mounted state of the optical film thickness meter
on the thin film forming apparatuses 1 and 2 will be described.
The thin film forming apparatus 1 illustrated in FIG. 1 is a
sputtering (magnetron sputtering) device provided with a
rotary-drum holder 33 and includes at least a vacuum container 31,
the rotary-drum holder 33 as a substrate holder on which the actual
substrate S is mounted, sputtering means 35 provided opposite to
each other outside the rotary-drum holder 33, and an unshown
sputter gas supply means.
The vacuum container 31 is made of stainless steel usually used in
a known thin film forming apparatus and is a hollow body having a
substantially rectangular solid shape. Also, on the side face side
of the vacuum container 31, that is, on the radial direction side
of the rotary-drum holder 33 of the vacuum container 31, the
measurement window 25 is formed.
The rotary-drum holder 33 is formed substantially cylindrically and
is arranged with the rotary shaft directed in the vertical
direction of the vacuum container 31. The rotary-drum holder 33 has
a function as holding means for the actual substrate S, and the
actual substrates S are mounted in a juxtaposed manner on the outer
peripheral face of the rotary-drum holder 33 through a substrate
holder, not shown, or the like.
Since an opening (not shown) having a predetermined size is formed
in a portion of the rotary-drum holder 33 where the actual
substrate S is mounted, the measurement light having passed through
the actual substrate S can enter the inside of the rotary-drum
holder 33. The rotary-drum holder 33 may be formed in a hollow
prism shape.
The sputtering means 35 is formed of a pair of targets, a pair of
magnetron sputter electrodes, which hold the targets, and a power
supply device (none of them is shown). The target gas has a plate
shape and is installed such that the longitudinal direction of the
target is parallel with a rotation axis of the rotary-drum holder
33.
In the periphery of the sputtering means 35, the sputter gas supply
means, which supplies a sputter gas such as argon, is provided. If
an AC voltage is applied from the power supply to the magnetron
sputter electrode in a state in which the periphery of the target
becomes an inactive gas atmosphere, a part of the sputter gas in
the periphery of the target emits electrons and is ionized. This
ion is accelerated and collides against the target so that atoms
and particles (if the target is niobium, niobium atoms or niobium
particles) on the surface of the target are knocked out. The
niobium atoms and niobium particles are film material substances
(deposition substances), which is a material of the thin film, and
adheres to the surface of the actual substrate S, and the thin film
is formed.
In the thin film forming apparatus 1, if the rotary-drum holder 33
is rotated, the actual substrate S held on the outer peripheral
surface of the rotary-drum holder 33 revolves and repeatedly moves
through two positions facing the sputtering means 35. Then, since
the actual substrate S revolves as above, sputtering treatment by
the sputtering means 35 is sequentially performed repeatedly, and
the thin film is formed on the surface of the actual substrate
S.
It may be so configured that plasma generating means is mounted on
the thin film forming apparatus 1 to conduct a pretreatment process
of applying plasma treatment to the surface of the actual substrate
S before the thin film is formed or a post-treatment process of
applying the plasma treatment to the surface of the actual
substrate S after the thin film is formed, at the same time as
formation of the thin film. It is needless to say that another film
forming means may be used instead of the sputtering means 35 in the
configuration.
In the thin film forming apparatus 1, the optical film thickness
meter according to the present invention is configured such that
the outgoing light L1 is radiated from the measurement window 25
formed in a part of the vacuum container 31 toward the actual
substrate S and the reflection light L2, which was the outgoing
light L1 having passed the actual substrate S, reflected by the
reflection mirror 17 installed on the back side of the actual
substrate S can pass through the actual substrate S again.
Specifically, the other end portion of the optical fiber 13 and the
spherical achromatic lens 15 connected to the light projector 11
and the light receiver 19 are disposed outside the vacuum container
31, and the reflection mirror 17 is fixed to the back side of the
actual substrate S and also at a position inside the rotary-drum
holder 33. Since the opening portion is formed in the rotary-drum
holder 33 at the position where the actual substrate S is mounted,
the outgoing light L1 having passed through the actual substrate S
can be made to pass through the opening portion of the rotary-drum
holder 33 and to be reflected by the reflection mirror 17 disposed
inside thereof.
As described above, by mounting the optical film thickness meter,
the optical film thickness and optical characteristics and the like
of the actual substrate S mounted on the rotary-drum holder 33 can
be measured even during film formation. Specifically, the
rotary-drum holder 33 is measured for the film thickness or the
like at a predetermined position where the measurement portion of
the actual substrate S is overlapped with the optical axis of the
measurement light. The actual substrate S is disposed so as to have
an inclination angle with respect to the optical axis of the
measurement light.
In the thin film forming apparatus 1, the reflection mirror 17 is
fixed to the back side of the actual substrate S and also at a
position inside the rotary-drum holder 33. Thus, the reflection
mirror 17 is hardly susceptible to stains and an influence of stray
light from plasma discharge during sputtering, which is
advantageous.
Also, the reflection mirror 17 may be mounted on a plurality of the
actual substrates S. That s, if the actual substrate S and the
reflection mirror 17 are assembled in a pair, a plurality of
measurements can be made for each of the actual substrates S for
the film thickness and optical characteristics of the actual
substrate S at a predetermined position corresponding to the
position of the outgoing light L1. By configuring as above, by
rotating the rotary-drum holder 33 so as to arrange the actual
substrate S at a predetermined position, the plurality of actual
substrates S in a state mounted on the rotary-drum holder 33 can be
measured for the optical film thickness by allowing the measurement
light to sequentially pass therethrough. Thus, the film thicknesses
of the plurality of actual substrates S can be measured
simultaneously, and a thin film forming apparatus capable of
measurement of the optical film thickness with higher accuracy can
be obtained.
Subsequently, the thin film forming apparatus 2 illustrated in FIG.
2 is a deposition device provided with a rotary holder 43 disposed
in a vacuum container 41 and includes at least a dome-shaped rotary
holder 43 as a substrate holder on which the actual substrate S is
mounted and deposition means 45 provided on the lower side
oppositely to the rotary holder 43. Also, in the thin film forming
apparatus 2 in this embodiment, a correcting plate 47 is disposed
at a position between the rotary holder 43 and the deposition means
45.
The vacuum container 41 is made of stainless steel usually used in
a known thin film forming apparatus and is a hollow body having a
substantially rectangular solid shape. Also, on the upper side of
the rotary holder 43, the measurement window 25 is formed.
The rotary holder 43 is formed substantially in the dome shape and
arranged in the vacuum container 41 with the rotary shaft directed
in the vertical direction and has a function as substrate holding
means, and a plurality of the actual substrates S can be attached
to the rotary holder 43 through a mounting jig, not shown. In the
portion where the actual substrate S of the rotary holder 43 is
mounted, an opening portion having a predetermined size (not shown)
is formed.
The deposition means 45 is installed at a position opposite to the
rotary holder 43 on the lower side of the vacuum container 41 and
includes a deposition substance contained in a melting pot and an
electron beam source or a high-frequency coil for heating the
deposition substance and the like. It is needless to say that a
sputter source formed of a target, an electrode, and a power supply
may be used as the deposition means.
The correcting plate 47 is a substantially plate-shaped member,
which corrects a difference in the film thickness on the actual
substrate S caused by a mounting position of the rotary holder 43
and is fixed in the vicinity of the vacuum container 41. As a
result, when a thin film is to be formed on the actual substrate S,
by partially preventing accumulation of a vaporized substance
vaporized from the deposition means 45 toward the actual substrate
S, the film thickness can be corrected. In the thin film forming
apparatus 2, the vaporized substance vaporized from the deposition
means 45 accumulates on the actual substrate S mounted on the
rotary holder 43 so that a film is formed. At this time, by means
of the rotation of the rotary holder 43 and the correcting plate
47, a difference in the film thickness by the position of the
actual substrate S is corrected.
In the thin film forming apparatus 2, the optical film thickness
meter according to the present invention is configured such that
the outgoing light L1 is radiated from the measurement window 25
formed in a part of the vacuum container 41 toward the actual
substrate S, and the outgoing light Li having passed through the
actual substrate S is reflected by the reflection mirror 17
installed on the correcting plate 47 on the lower side of the
actual substrate S so as to be made the reflected light L2, which
is passed through the actual substrate S again.
Specifically, the optical fiber end portion 14 and the spherical
achromatic lens 15 connected to the light projector 11 and the
light receiver 19 are disposed outside the vacuum container 41, and
the reflection mirror 17 is fixed at a position on the lower side
of the actual substrate S and on the upper side of the correcting
plate 47. Since the opening portion is formed in the rotary holder
43 at the position where the actual substrate S is mounted, the
outgoing light L1 having passed through the actual substrate S can
be made to pass through the opening portion in the rotary holder 43
and to be reflected by the reflection mirror 17 disposed on the
lower side thereof.
As described above, by mounting the optical film thickness meter,
the optical characteristics such as the film thickness of the
actual substrate S mounted on the rotary holder 43 can be measured
even during the film formation. Specifically, measurement of the
film thickness and the like is made with the rotary holder 43 at a
predetermined position where the measurement portion of the actual
substrate S is overlapped with the optical axis of the measurement
light.
The optical film thickness meter is disposed so that the actual
substrate S has an inclination angle with respect to the optical
axis of the measurement light.
Also, since the reflection mirror 17 is mounted on the actual
substrate S side of the correcting plate 47, the actual substrate S
disposed on a measurement circumference can be measured in a fixed
state, whereby stable measurement can be made.
In the thin film forming apparatus 2, the reflection mirror 17 is
mounted on the same side as the actual substrate S relative to the
correcting plate 47, and since it is likely that the deposition
substance from the deposition means 45 sneaks around and adheres to
the reflection surface of the reflection mirror 17, a
sneaking-preventive glass can be mounted immediately in front of
the reflection mirror 17. Moreover, the sneaking-preventive glass
may be surrounded by a cylindrical hood in order to prevent
adhesion of the deposition substances to the sneaking-preventive
glass.
The sneaking-preventive glass is preferably replaced regularly.
Also, the sneaking-preventive glass is more preferably disposed
having an angle with respect to the optical axis of the measurement
light similarly to the actual substrate S.
Also, in the thin film forming apparatuses 1 and 2, when
measurement is to be made by the optical film thickness meter, the
actual substrate S needs to be accurately aligned to the
measurement position. Thus, both the thin film forming apparatuses
1 and 2 are provided with rotation control means which stops the
rotary-drum holder 33 or the rotary holder 43 at a measurement
position. As the rotation control means, a known device can be
applied and can be configured by including a positional sensor and
a motor which can monitor and control a rotational angle all the
time, for example.
In the thin film forming apparatuses 1 and 2, the measurement
window 25 is also disposed with a predetermined angle with respect
to the optical axis of the measurement light. This is because of
the same reason as disposition of the actual substrate S with
inclination at a certain angle. Thus, light reflected by the glass
member of the measurement window 25 can be also prevented from
being inputted into the light receiver 19 side.
The optical film thickness meter of the present invention will be
described below by referring to FIGS. 3 to 8.
Measurements or calculation examples illustrated below are results
in the thin film forming apparatus 1 on which the optical film
thickness meter according to the present invention is mounted, but
advantages and the like which can be obtained from the measurement
results can be also applied to the thin film forming apparatus 2 as
they are.
FIG. 3 is a graph illustrating a relationship between a reflection
mirror angle .theta. to the optical axis and the intensity of the
measurement light and a measurement result of the reflection mirror
angle .theta. from -6 to +6.degree..
Here, the reflection mirror angle .theta. of the reflection mirror
17 is an angle formed by a perpendicular line to the reflection
surface of the reflection mirror 17 and the optical axis of the
measurement light.
As obvious from FIG. 3, when the angle .theta. of the reflection
mirror 17 is 0.degree., the light amount of the reflection light
becomes the maximum value. In FIG. 3, data converted as the
reflectivity of the reflection mirror 17 at 100% is shown.
Also, though the measurement light intensity of the reflection
light becomes the maximum when the reflection mirror angle .theta.
is 0.degree., the measurement light intensity is 82 to 87% or more
at the reflection mirror angle .theta. of .+-.1.0.degree. with
respect to the reflection mirror angle .theta.=0.degree., and if
the reflection mirror angle .theta. is .+-.0.6.degree., the
measurement light intensity is 94 to 96% or more. In FIG. 3, the
light amount of the reflection light is a value expressed in a rate
of the light amount measured in the reflection mirror 17 (the light
amount of the reflection light L2) with respect to the light amount
of the outgoing light L1 in percentage.
Also, the allowable reflection mirror angle .theta.=-5.0 to
+5.0.degree. of the reflection mirror 17 is a value changing in
accordance with the distance between the reflection mirror 17 and
the spherical achromatic lens 15 or the optical fiber end portion
14. That is, if the distance between the reflection mirror 17 and
the spherical achromatic lens 15 or the optical fiber end portion
14 becomes longer, the allowable reflection mirror angle .theta. of
the reflection mirror 17 becomes small.
In the thin film forming apparatus 1, the distance between the
reflection mirror 17 and the spherical achromatic lens 15 is
approximately 60 to 350 mm.
FIG. 4 is an explanatory diagram illustrating inclination of the
substrate and a rate change of the measurement light and
illustrates the inclination of the actual substrate S, a path of
the measurement light (outgoing light and reflection light), and a
rate change of the light, in which FIG. 4A illustrates a case of
the inclination angle .alpha. of the actual substrate S=0.degree.
(no inclination), and FIG. 4B illustrates a case of the inclination
angle .alpha. of the actual substrate S that has a certain value.
Here, the inclination angle .alpha. of the actual substrate S is an
angle formed by a perpendicular line to the film formation surface
of the actual substrate S and the optical axis of the measurement
light.
The light amounts in FIGS. 4 are indicated with the light amount
measured in a state in which the actual substrate S is not mounted
as 100%. Also, the reflectivity of the reflection mirror 17 is
assumed to be 80%, here.
First, the path of the measurement light with the inclination angle
.alpha. of the substrate=0.degree. and the rate change of the light
illustrated in FIG. 4A will be described.
The light incident from the measurement window 25 of the vacuum
container 31 (the outgoing light L1) passes through the actual
substrate S. At this time, supposing that the total light amount of
the incident light (the outgoing light L1) is "100", the light is
reflected on the surfaces on both sides of the actual substrate S
by 4.25% each without passing through the substrate (total light
amount is 8.5). The light with the light amount of 8.5 is emitted
from the measurement window 25 as reflection light L2-1. Therefore,
the light amount passing through the actual substrate S becomes
91.5. The transmission light with the light amount of 91.5 is
reflected by the reflection mirror 17 disposed on the back side of
the actual substrate S. This turned back reflection light passes
through the actual substrate S again and similarly, considering the
reflectivity of 8.5% in total, the remaining 91.5% passes through
the actual substrate S. That is, the light amount of 83.7 (the
first transmission light 91.5.times.second transmissivity of 91.5%
by turning back from the reflection mirror 17) is emitted as L2-2
from the measurement window 25. At this time, the reflectivity of
the reflection mirror 17 is ignored because 100%-baseline
measurement is conducted in a state without the actual substrate S
(only reflection of the reflection mirror 17) before measurement of
the actual substrate S.
When the turned back reflection light passes through the actual
substrate S, if the light amount of 7.78 reflected by the actual
substrate S (91.5.times.8.5%) is reflected by the reflection mirror
17 again, the light amount of 6.22 (7.78.times.reflection mirror
reflectivity of 80%) travels toward the actual substrate S again.
This re-reflection light with light amount of 6.22 is also
reflected by the actual substrate S by 4.25% each or 8.5% in total,
and the light amount of 5.69 (6.22.times.91.5%) is emitted from the
measurement window 25 as L2-3.
That is, the light emitted from the measurement window 25 is L2-1
to 3, in which the reflection light of the actual substrate S is
mixed.
That is, the light incident from the measurement window 25 (the
outgoing light L1) is roughly divided as follows (since the
multiple reflection light of the reflection light L2-4 or more is
micro, it is ignored in this model):
(1) Reflection light L2-1: 8.5 (double-sided reflection light by
the actual substrate S)
(2) Reflection light L2-2: 83.7 (light passing through the actual
substrate S twice by reflection of the reflection mirror 17)
(3) Reflection light L2-3: 5.69 (light passing through the actual
substrate S by re-reflection of the reflection mirror 17)
Therefore, among the light incident from the measurement window 25
(the outgoing light L1), the light amount becomes approximately
97.89 (8.5+83.7+5.69) and travels toward the measurement window 25
of the vacuum container 31 as the reflection light L2. It is
because all the reflected light beams travel along the same path
since the inclination angle of the actual substrate is
0.degree..
That is, in the case of the inclination angle of the actual
substrate S at 0.degree., approximately 14.19 (8.5+5.69) among the
light inputted into the light receiver 19 (the reflection light L2)
is the reflection light of the actual substrate S. Therefore,
supposing that the inclination angle of the actual substrate S is
0.degree., the reflection light L2 incident to the light receiver
19 includes the light beam having passed a path other than the
desired one by 10% or more, which causes a measurement error.
Subsequently, the path of the measurement light and the rate change
of the light if the inclination angle of the substrate has a
predetermined value illustrated in FIG. 43 will be described.
Similarly to the above FIG. 4A, transmission and reflection of the
outgoing light L1 and the reflection light L2 occurs, but since the
actual substrate S is inclined with a predetermined angle, the
light of 8.5% reflected on the surface of the actual substrate S is
reflected in the direction according to the inclination of the
actual substrate S. Therefore, if the inclination angle of the
actual substrate S is a predetermined value or more, the light beam
reflected on the surface of the actual substrate S does not travel
toward the light receiver 19.
Also, in the reflection light L2 reflected by the reflection mirror
17, the light reflected by the actual substrate S is also reflected
in the direction according to the inclination of the actual
substrate S and does not travel toward the light receiver 19,
either.
That is, if the actual substrate S is inclined by a predetermined
angle, only the light beam (with the light amount of 83.7) having
passed through the actual substrate S twice is inputted into the
light receiver 19. Therefore, there are few factors to cause an
error, and measurement with higher accuracy can be expected.
FIG. 5 are graphs illustrating a relationship between the substrate
angle and the measurement light intensity and illustrate
measurement results of the relationship between the inclination
angle .alpha. of the actual substrate S and the light amount of the
reflection light, in which FIG. 5A is a measurement result of the
inclination angle .alpha. of -6 to +6.degree., and FIG. 5B is a
graph illustrating the result of FIG. 5A in an enlarged manner for
the inclination angle .alpha.=+3 to +5.5.degree.. The light amounts
in FIG. 5 use data measured in a state in which the actual
substrate S is not mounted as a reference.
As obvious from FIG. 5A, at the inclination angle a of the actual
substrate S=0.degree., the light amount of the reflection light
becomes the maximum value. That is because, as described in FIG.
4A, the light beam reflected on the front and back faces of the
actual substrate S is also included.
If the angle of the actual substrate S is inclined, the light beam
reflected on the surface of the actual substrate S is reflected in
the direction according to the inclination of the actual substrate
S, and the light amount measured by the light receiver 19 decreases
along with the inclination angle of the actual substrate S. In a
region with the inclination angle of approximately 4.5.degree. or
more, the light amount shows a substantially constant value. That
is because, as described in FIG. 48, the light reflected on the
front and back faces of the actual substrate S is no longer taken
into the light receiver 19.
Since it is known from FIG. 5B that a constant value is shown at
the inclination angle of approximately 4.5.degree. or more, it is
preferable that the inclination angle of the actual substrate S is
set at 4.5.degree. or more. Here, since the similar effect is
obtained in whatever direction the actual substrate S is inclined,
the inclination angle is an absolute value of the angle with
respect to the surface orthogonal to the optical axis of the
measurement light.
That is, the inclination angle of the actual substrate S is
preferably set to .+-.4.5.degree. or more.
Also, the inclination angle of the actual substrate S is preferably
the minimum within a range in which the light amount shows a
constant value. Here, according to FIG. 5B, though slight
inclination is found in the light amount change at the inclination
angle of approximately 4.5.degree., the change in the light amount
is no longer found at the inclination angle=5.degree. or more.
Also, the inclination angle of the actual substrate S is a value
changing in accordance with the distance between the actual
substrate S and the reflection mirror 17 or between the actual
substrate S and the spherical achromatic lens 15 or the optical
fiber end portion 14. For example, if the distance between the
actual substrate S and the spherical achromatic lens 15 or the
optical fiber end portion 14 becomes longer, the allowable
inclination angle of the actual substrate S becomes a small
value.
As described above, in the thin film forming apparatus 1, the
distance between the reflection mirror 17 and the spherical
achromatic lens 15 is approximately 60 to 350 mm.
FIGS. 6 to 8 are measurement examples by the optical film thickness
meter of the present invention, and they illustrate the result of
measurement of the actual substrate S (BK-7 substrate) and the
optical filter F by the optical film thickness meter in comparison
with the measurement result of one transmission. In all the
examples described below, measurement was made with the inclination
angle of the actual measured substrate S=5.degree..
EXAMPLE 1
FIG. 6 is a graph illustrating a transmissivity measurement result
of a BK-7 substrate. The X-axis indicates a measurement wavelength
and the Y-axis indicates the light amount (transmissivity). FIG. 6
illustrates a transmissivity measurement result of two
transmissions by the optical film thickness meter according to the
present invention, a transmissivity measurement result of one
transmission by a spectrophotometer SolidSpec3700 (by Shimadzu
Corporation), and a converted value obtained by converting the data
of one-transmission measurement to two-transmission
measurement.
As obvious from FIG. 6, the BK-7 substrate has substantially flat
transmissivity characteristics (optical characteristics) over the
entire measured wavelength regions and the measured value of
two-transmission and the converted value obtained by converting the
one-transmission to the two-transmission show substantially the
same value over the entire wavelength regions. This illustrates
that with a simple configuration in which the reflection mirror 17
is arranged in the vacuum container 31, the optical film thickness
meter according to the present invention has a large change amount
with respect to the 100% light amount, that is, the control
accuracy of the film thickness measurement can be improved.
EXAMPLE 2
FIG. 7 is a graph illustrating a transmissivity measurement result
of an IR cut filter. The IR (infrared) cut filter is an optical
filter F in which Nb.sub.2O.sub.5/SiO.sub.2 is laminated on the
BK-7 substrate. In FIG. 7, similarly to FIG. 6, the X-axis and the
Y-axis also indicate the measurement wavelength and transmissivity,
respectively, and the measurement result (two-transmission) by the
optical film thickness meter according to the present invention,
the measurement (one-transmission) by the spectrophotometer, and a
value (converted value) obtained by converting the one-transmission
data to the two-transmission one are shown.
According to FIG. 7, regarding the IR cut filter, the
transmissivity in the infrared wavelength region at approximately
700 nm or more shows a value in the vicinity of 0%. In this
measurement by the IR cur filter, the measured value of the
two-transmission and the converted value obtained by converting the
one-transmission to two-transmission also show substantially the
same value over the entire wavelength region. Therefore, in the
measurement with the IR cut filter, too, the optical film thickness
meter according to the present invention can be considered to have
measurement accuracy at least equal to the prior-art
one-transmission optical film meter.
FIG. 8 compares the characteristics of the optical film thickness
meter of the present invention with the prior-art measurement
method and compares the calculation result by the optical film
thickness meter according to the present invention and the
calculation result by the prior-art one-transmission. For the
calculation (simulation), optical calculation theory software sold
in the market is used.
EXAMPLE 3
FIG. 8 is a graph illustrating a change in the light amount in the
optical film thickness at the wavelength of 520 nm by elapsed time
when a SiO.sub.2 single-layer film is formed, which shows a
calculation result of a change in the light amount of the SiO.sub.2
single-layer film filter, and compares the one-transmission
calculation result with the two-transmission calculation result of
the SiO.sub.2 single-layer film filter by the optical film
thickness meter according to the present invention. The SiO.sub.2
single-layer film filter is an optical filter F in which a
SiO.sub.2 single-layer film is formed on BK-7. The X-axis indicates
the film forming time (in proportion to the film thickness) and the
Y-axis indicates the transmission light amount. Also, the
light-amount change calculation is a value at the wavelength of 520
nm.
As illustrated in FIG. 8, regarding the two-transmission calculated
value by the optical film thickness meter according to the present
invention (two transmission) and the one-transmission calculated
value (one transmission), the change amount in the two-transmission
in the present invention is bigger both in the transmissivity and
transmission light amount, and measurement accuracy is improved
more than the prior-art example by this increased change
amount.
In FIG. 8, by comparing the calculation result of the measured
value by the optical film thickness meter according to the present
invention and the calculation result of the measured value by one
transmission, it is shown that the change rate in the measurement
by the optical film thickness meter of the present invention is
higher. A difference in the change amounts is approximately 1.6 to
1.8 times. This is because the change amount becomes bigger by
reduction in the transmissivity caused by two transmissions through
the actual substrate S. Since the change amount in the measured
value is large, measurement accuracy can be improved, and the
optical film thickness meter according to the present invention can
be considered to have measurement accuracy more excellent than the
prior-art one-transmission optical film thickness meter.
* * * * *